Charging blocks for iPhone 13

My family recently upgraded our phones - we now have iPhone 13 and 13 Mini. The salesperson at Verizon told us that, with 13s and above, it is important to always use a charging block that is 20 Watts or higher, and that if we use charging blocks with lower wattage (like all of our older iPhone charging accessories), we'll damage the batteries on the new phones. Fact, or fiction? I can't find anything about this in any of Apple's support documentation.